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JIT: REX.W prefix jmp [abs32] form used for tailcalls - #136845
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Like other instructions emitted in the epilog this one must be rex.w prefixed for the unwinder to recognize it as being part of an epilog. Also avoid using APX registers for the target register; encoding those will require prefixes that also are not recognized by the unwinder. Fix dotnet#129071
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch |
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APX will require UnwindInfo v3. UnwindInfo v3 does not disassemble the epilogs, and thus it does not have restrictions around instructions encodings. |
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Good point! Undid that. |
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November 3, 2026 07:22
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cc @dotnet/jit-contrib PTAL @adamperlin |
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Like other instructions emitted in the epilog this one must be rex.w prefixed for the unwinder to recognize it as being part of an epilog.
Fix #129071
I did have Copilot validate based on the instructions in #129071 (comment), and it did see corruptions with the baseline JIT but not with the fixed JIT. No test added since it is very difficult to force the JIT to emit this form of epilog jump.